The present invention relates to outdoor building materials, in general, and to solar control thermoplastic polymer sheets for roofing and cladding, in particular.
In the industrial and residential building sectors there is an existing market for light-transmitting sheet materials that allow natural light to enter the building or covered space One of the requirements for light-transmitting sheets for building is a service temperature of up to 80-90xc2x0 C. and down to xe2x88x9230xc2x0 C. Furthermore, the sheet should be UV resistant for 20-50 years in extreme radiation conditions, an issue which is made more important by the ozone hole problem. The light transmission (LT %) should be controllable, with typical values of 15-50%. The sheet should have a low Total Solar Transmission (STt), which is the percent of incident solar radiation transmitted by the sheet, including both the solar transmission and the part of the solar absorption reradiated inward. As well, the sheet should have a low Shading Coefficient (SC), which is a measure of the total solar transmission relative to that of standard glass. Preferably, the ratio of LT % to STt of the sheet is high, signifying maximum light transmission with minimum heat. Finally, the sheet should be resistant to corrosion and environmentally friendly.
Existing light-transmitting sheets are shown in FIGS. 1A, 1B, 1C and 1D, to which reference is now made. FIG. 1A is a schematic illustration of a cross-section of a prior art sheet 10 which is clear and not tinted. The sheet 10 is composed of clear, untinted material 12 such as polycarbonate (PC), polyvinylchloride (PVC) or fiberglass. The sheet 10 allows most of the incident ultraviolet (UV), visible and near infrared (NIR) radiation, shown as solid lines, to pass through it unabsorbed. However the transmitted solar radiation, shown as dashed lines, then heats the covered space under the sheet 10, which causes thermal stress on people and increases the work to be done by air conditioning systems.
FIG. 1B is a schematic illustration of a cross-section of a prior art, sheet 14 which is clear and tinted, the sheet material comprising a clear polymer 16 with an absorbing pigment 18. Examples of the sheet material are tinted glass and tinted PC. Some of the incident radiation, shown by solid lines, is absorbed by the pigment 18 and some is transmitted. The transmitted radiation, shown by dashed lines, heats the covered space. The absorption, shown by squiggles, causes the temperature of the sheet itself to rise. The heated sheet subsequently remits the energy at far infrared (FIR) wavelengths, as shown by the curvy lines. The portion of the reemitted FIR radiation transmitted inward contributes to further heating of the covered space.
FIG. 1C is a schematic illustration of a cross-section of a prior art glass sheet 20, coated with a reflective coating 22 that reflects part of the incident radiation, shown by solid lines, rather than absorbing it. A protective layer 24 coats the reflective coating 22, and protects it from corrosion. However, the reflective coating 22 is still susceptible to corrosion on the edges of the sheet 20 and on the surface in the event that some of the protective layer 24 has been removed, scratched or dented. Reflective glass is brittle and is unavailable as a corrugated roofing material.
FIG. 1D is a schematic illustration of a cross-section of a prior art plastic sheet 20xe2x80x2, coated with a metallic coating 22xe2x80x2 that reflects part of the incident radiation, shown by solid lines, rather than absorbing it. A protective layer 24xe2x80x2 coats the metallic coating 22xe2x80x2, and protects it from corrosion. However, the metallic coating 22xe2x80x2 is still susceptible to corrosion on the edges of the sheet 20xe2x80x2 and on the surface in the event that some of the protective layer 24xe2x80x2 has been removed, scratched or dented. The metallic coating 22xe2x80x2 can be applied to flat lo sheets only and cannot be applied to corrugated sheets.
German Patent DE19520062 to Moench describes a method of manufacturing a plastic sheet using metal particles, the resulting sheet reflecting IR rays but allowing visible light and UV rays to pass through it. Moench describes aluminum or bronze as the ideal choice for the metal particles. There are several problems with sheets according to Moench. First of all, it is well known in the art that aluminum reflects IR, visible and UV light in the same proportion. Therefore, it is not possible that a plastic sheet containing particles of aluminum will selectively reflect IR light and let visible and UV light to pass through it. Bronze will reflect slightly more IR light than it reflects visible and UV light, but the difference from aluminum is not significant. Secondly, the purpose of the sheet is as a transparent building material that controls how much the building is heated by light However, it is well known that all light entering a building, IR, visible and UV will contribute to the heat inside the building. Therefore, a sheet according to Moench which is permeable to visible and UV light will still contribute to the heat inside the building. Thirdly, the metal particles according to Moench are spherical, which have low reflectance efficiency.
It is an object of the present invention to provide a light-transmitting, thermoplastic polymer sheet material that can be used as an outdoor building material and which overcomes the limitations and disadvantages of existing materials.
There is provided in accordance with a preferred embodiment of the present invention a rigid light transmitting thermoplastic polymer sheet having an upper face. The sheet includes transparent thermoplastic polymer having flakes of metal pigment dispersed therein. The flakes are oriented coplanar to the upper face.
There is also provided in accordance with another preferred embodiment of the present invention a rigid light transmitting thermoplastic polymer sheet including a first transparent thermoplastic polymer layer and a second UV-protective transparent thermoplastic polymer layer co-extruded with the first layer. The second layer is formed on top of the first layer. The sheet also includes metal pigment dispersed within at least one of the first and second layers.
In accordance with a preferred embodiment of the present invention, the metal pigment is dispersed within the first transparent thermoplastic polymer layer.
Alternatively, in accordance with a preferred embodiment of the present invention, the metal pigment is dispersed within the second UV-protective transparent thermoplastic polymer layer.
Furthermore, in accordance with a preferred embodiment of the present invention, the thermoplastic polymer is one of a group including: polycarbonate (PC), polyvinylchloride (PVC), polymethylmethacrylate (PMMA), polyethylenterphtalateglycol (PETG) and polystyrene (PS).
Additionally, in accordance with a preferred embodiment of the present invention, the sheet is one of a group of a flat sheet, a corrugated sheet and a multi-wall sheet.
Moreover, in accordance with a preferred embodiment of the present invention, the sheet has an upper face and flakes of the metal pigment are oriented coplanar to the upper face.
There is provided, in accordance with a preferred embodiment of the present invention, a method for production of a rigid light transmitting thermoplastic polymer sheet, the method including the steps of treating metal pigment flakes thereby to increase their surface energy, and feeding a thermoplastic polymer material and the metal pigment flakes into an extrusion line, thereby forming a melt. The method includes as well the steps of extruding the melt through an extrusion die, and solidifying the melt into a rigid sheet
Moreover, in accordance with a preferred embodiment of the present invention, the method of production includes the step of thermoforming the rigid sheet.
Furthermore, in accordance with a preferred embodiment of the present invention, the step of thermoforming is performed on-line or off-line.
Additionally, in accordance with a preferred embodiment of the present invention, the thermoplastic polymer material is one of a group including: PC, PVC, PMMA, PETG and PS.
There is provided, in accordance with a preferred embodiment of the present invention, a method for production of a rigid, light-transmitting thermoplastic polymer sheet, the method including the steps of treating metal pigment flakes thereby to increase their surface energy, feeding a first thermoplastic polymer material into a first extrusion line, feeding a second thermoplastic polymer material into a second extrusion line, and feeding the metal pigment flakes into at least one of the extrusion lines. The method includes as well the steps of co-extruding the first thermoplastic polymer material and the second thermoplastic polymer material into a melt, whereby the second thermoplastic polymer material forms a layer on the first thermoplastic polymer material, extruding the melt through an extrusion die, and solidifying the melt into a rigid sheet.